JPH03162116A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To obtain the surface acoustic wave device having a large suppression quantity in a stopping area and a high performance by reducing the influence of an electromagnetic induction on a pattern with regard to surface acoustic waves connected in a multistage. CONSTITUTION:To a piezoelectric substrate 21, resonator filters 22-24 are connected electrically in a three-stage cascade connection. In such a state, extending from a first excitation (receiving) electrode of the resonator filter 22 of a first stage to a third excitation (receiving) electrode of the resonator filter 24 of a third stage, all of them are not connected electrically, therefore, a direct wave on an electrode pattern extending from the resonator filter 22 of a first stage to the resonator filter 24 of a third stage is prevented, and also, a current loop also becomes small, and moreover, a current flowing into a positive electrode of each electrode, and a current flowing out of a load become reverse in the same direction. Accordingly, the influence of an electromagnetic induction on the pattern is reduced. In such a way, the suppression quantity in a stopping area can be secured enough.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a surface acoustic wave device, and particularly to its electrode structure.

(Prior Art) Generally, surface acoustic wave devices are widely used in the communication industry field from several tens of MHz to several hundred MHz, and surface acoustic wave filters are often used as band pass filters in this frequency band. .

By the way, a normal filter has a pass band that allows signals to pass and a stop band that does not allow signals to pass.

It is desirable that the amount of attenuation in the pass band be as small as possible, and the amount of suppression in the stop band be as large as possible. In particular, in low-loss filters used in PF stages for mobile communications, etc., the suppression amount in the stopband is required to be approximately 60 dB, and the attenuation amount in the passband must be approximately 4 to 5 dB. It is.

However, in the case of surface acoustic wave filters, it is very difficult to achieve this amount of suppression with only one filter stage, so conventionally, filters are connected in multiple stages.
An attempt was made to obtain the desired amount of suppression. However, when the filters are arranged in multiple stages, each of the multi-stage filters must be individually grounded, resulting in an increase in the number of bonding wires.

As the number of bonding wires increases, direct waves may jump between the bonding wires, resulting in generation of unnecessary signals. In addition, the bonding wires may come into contact with each other, and this goes against the trend of miniaturizing surface acoustic wave devices. Therefore, the inventors of the present invention attempted to reduce the number of grounding bonding wires by using a common ground for each stage of the filter. However, in this case,
There are cases where the pattern wiring in each stage is easily affected by electromagnetic induction, which becomes a serious problem.

Next, such a surface acoustic wave device will be explained with reference to FIG. 4. FIG. 4 shows a resonator filter in which three resonator filters are connected vertically.

In this resonator filter, in order to reduce the number of bonding wires, a negative comb-shaped electrode (hereinafter referred to as negative electrode) (71) of the first excitation electrode and a negative electrode (71) of the second receiving electrode are used.
2) and the negative electrode (73) of the third excitation electrode are electrically connected, and the negative electrode (74) of the first receiving electrode and the second
The negative electrode (75) of the excitation electrode and the negative electrode (75) of the third receiving electrode
76) is electrically connected.

In addition, the negative electrode (75) of the third excitation electrode and the ground terminal (77
) is electrically connected to the negative electrode of the first receiving electrode (
74) and the ground terminal (78) are electrically connected. However, in the case of such an electrode configuration, electromagnetic induction occurs due to the factors described below, and as a result, it is not possible to secure a sufficient amount of suppression in the stopband. First, because the first to third electrodes are all electrically connected, the electromagnetic signal is transmitted from the first electrode to the third electrode much faster than the surface wave is excited and propagates from the first electrode to the third electrode. It is transmitted from the first electrode to the third electrode. This results in
Direct wave guidance occurs and the stopband characteristics deteriorate. Second, there is an effect due to the current generated when exciting or receiving surface waves. In other words, for each stage of filters,
A current loop is formed on the excitation electrode side and a current loop on the receiving electrode side, respectively, but in order to minimize the influence of electromagnetic induction, it is desirable that the size of these loops be as small as possible. This principle is the same as that of coaxial cables and feeder lines. However, in the case of this pattern, this current loop is very large, so it is easily affected by electromagnetic induction.

For the reasons explained above, conventional surface acoustic wave devices are susceptible to the influence of induction, and therefore the amount of suppression in the stopband is insufficient. As a solution to this problem, the present inventors attempted to further increase the number of filter stages, but in this case, the chip size increased due to the increase in pattern area.
This leads to complicated wiring.

(Problems to be Solved by the Invention) The present invention has been made in view of the above-mentioned problems, and when connecting surface acoustic wave filters in multiple stages on a piezoelectric substrate,
It is an object of the present invention to provide a surface acoustic wave device that can secure a sufficient amount of suppression in a stopband by reducing the influence of electromagnetic induction.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above-mentioned problems, the surface acoustic wave device of the present invention includes a positive comb-shaped electrode and a signal terminal constituting the excitation electrode of the first stage surface acoustic wave element. are electrically connected, and the negative electrode comb teeth tltt4, which constitutes the excitation electrode of the first stage surface acoustic wave element, and the connection terminal are electrically connected, and constitute the receiving electrode of the final stage surface acoustic wave element. The positive comb-shaped electrode and the signal terminal are electrically connected, and the negative comb-shaped electrode that constitutes the receiving electrode of the final stage surface acoustic wave element and the ground terminal are electrically connected. Excluding the excitation electrode of the surface acoustic wave element and the reception electrode of the final stage surface acoustic wave element, one set is composed of the excitation electrode of one surface acoustic wave element and the reception electrode of the other surface acoustic wave element adjacent thereto. Excitation t! ! It is characterized in that the same poles of the comb-tooth electrodes forming the poles and the comb-tooth electrodes forming the receiving electrode are electrically connected to each other.

(Function) By taking the above-mentioned means, the surface acoustic wave device of the present invention provides the following function.

■ In the surface acoustic wave elements from the first stage to the final stage, since electrical signals do not reach directly on the pattern, the influence of electromagnetic induction due to direct waves is prevented.

(2) Since the negative electrodes are connected only to the electrodes where the positive electrodes are connected, the current loop becomes small, and the influence of Wa induction due to the current loop can be prevented.

■ If the connection points of the 5 signal terminals and the ground terminals of the first stage and the final stage are set in a direction opposite to the piezoelectric substrate, the influence of direct waves will be further reduced.

■ By making the configuration shown in ■, the current flowing into the positive electrode of each electrode and the current flowing out from the negative electrode. Since the directions are the same and opposite, the influence of guidance is further reduced.

(Embodiment) An embodiment of the present invention will be described below with reference to the drawings.

In Figure 1, the surface acoustic wave device consists of LiTaO,...
Resonator filters (22), (23), and (24) are electrically connected in three stages vertically on a piezoelectric substrate (2l) such as LiNbO.

The negative pole (1) of the first receiving electrode of the first stage resonator filter (22), the negative pole (1) of the second excitation electrode of the second stage resonator filter (23), the first stage resonator filter ( 22) of the positive electrode of the first receiving electrode (hereinafter referred to as positive electrode) (
3), the positive electrode (4) of the second excitation electrode of the second stage resonator filter (23), the negative electrode 0 of the second receiving electrode of the second stage resonator filter (23), and the third stage resonance. Child filter (24
), the negative pole 0 of the third excitation electrode of the second stage resonator filter (23), the positive pole 0 of the second receiving electrode of the second stage resonator filter (23), and the positive pole of the third excitation electrode of the third stage resonator filter (24) ( 8) Toga AQ
It is electrically connected via a lead wire (25). Note that each electrode of the resonator filters (22), (23), and (24) and the reflective electrode (26) are made of AQ.

Next, the positive electrode ■ of the first excitation electrode of the first stage resonator filter (22) and the signal terminal (lO) of the stem (26) made of iron or the like are connected to a bonding wire (hereinafter referred to as a wire made of ) (11).Also, the first stage resonator filter (22)
The negative electrode (l2) of the first excitation electrode and the ground terminal (13) are electrically connected via a wire (14).

Further, the positive electrode (15) of the third receiving electrode of the third stage resonator filter (24) and the signal terminal (16) are connected to the wire (17).
), and the negative electrode of the third receiving electrode (
18) and a ground terminal (19) are electrically connected via a wire (20). Note that the connection points (21), (22), (23), and (24) between the wire and the terminal are as follows.
Each of them is in a direction opposite to the piezoelectric substrate (21).

(referred to as matter A) Also, the first stage resonator filter (22
), the negative pi (1) of the H electrode, the negative electrode 0 of the excitation electrode of the third stage resonator filter (24), and the ground terminal may or may not be electrically connected. Needless to say.

By adopting the above configuration, the surface acoustic waves are excited and the first excitation (receiving) electrode is not electrically connected from the first excitation (reception) electrode to the third excitation (reception) electrode. The electromagnetic signal travels faster from the electrode to the third excitation (reception) electrode than from the first excitation (reception) electrode to the third excitation (reception) electrode. Therefore, direct waves on the electrode pattern from the first stage resonator filter (22) to the third stage resonator filter (24) are prevented, and the current loop is also smaller than that shown in Fig. 4. becomes smaller. In addition, the current flowing into the positive electrode of each electrode,
The current flows from the negative electrode in the same direction and in the opposite direction. Therefore, in the surface acoustic wave device shown in FIG. 1, the influence of induction is reduced, and a filter with a large amount of suppression in the stop band can be realized.

Note that in the surface acoustic wave device shown in FIG. 1, even without the constituent requirements of matter A, the influence of direct waves is reduced compared to the surface acoustic wave device shown in FIG. 4.

Moreover, each resonator filter may be the same piezoelectric substrate or may be an individual piezoelectric substrate.

Next, another embodiment of the present invention will be described with reference to FIG.

FIG. 2 shows a surface acoustic wave device in which two stages of common camera filters are connected vertically on the same piezoelectric substrate.

The negative Vi (41) of the first receiving electrode of the first stage resonator filter (3l) and the second negative Vi of the second stage resonator filter (32)
Negative electrode of stage excitation electrode (42). What is the positive electrode (43) of the first stage receiving electrode of the first stage resonator filter (31) and the second excitation electrode (46) of the second stage resonator filter (32)? It is electrically connected by an AQ lead wire (33). The positive electrode (45) of the No. 1 excitation electrode of the first stage resonator filter (4l) and the signal terminal (46) implanted on the stem (34) are electrically connected via a wire (57). It is connected to the. The negative electrode (48) of the first excitation electrode of the first stage resonator filter (31) and the ground terminal (69) implanted on the stem (34) are electrically connected by a wire (50). ing.

Further, the positive 1'4it (41) of the second receiving electrode of the second stage resonator filter (32) and . The signal terminal (62) implanted on the stem (34) is electrically connected via a wire (53). Second stage resonator filter (32
) and the negative electrode (44) of the second receiving electrode of the stem (34).
It is electrically connected to a ground terminal (65) planted above via a wire (56).

As mentioned above, the surface acoustic wave device shown in FIG. 2 has the same effect as the surface acoustic wave device shown in FIG. Furthermore, the present invention is not limited to the above-described embodiment, and as shown in FIG. The negative electrode (44) of the electrode is connected to the lead wire (71), (
It goes without saying that the wiring may be routed via 72).

〔Effect of the invention〕

By adopting the above configuration, the surface acoustic wave device of the present invention can reduce the influence of electromagnetic induction on the pattern regarding the surface acoustic wave elements connected in multiple stages.
A high-performance surface acoustic wave device with a large amount of suppression in the stopband can be obtained.

[Brief Description of the Drawings] Fig. 1 is a schematic plan view showing one embodiment of the present invention, Figs. 2 and 3 are schematic plan views showing other embodiments of the present invention, and Fig. 4 is a conventional art. FIG. ■,■, (7), (8), ■L (15),
(41) , (43) , (45) , (46
)...Positive comb electrode (υ, ■, ■, ■, (12) , (18) , (
41), (42), (44). (48),
(71), (72), (73), (74),
(75), (76)...Negative comb electrode (21)...Piezoelectric substrate

Claims (4)

[Claims] (1) An elastic surface composed of an excitation electrode formed by crossing a positive comb-shaped electrode and a negative comb-shaped electrode, and a receiving electrode formed by crossing a positive comb-shaped electrode and a negative comb-shaped electrode. An elastic device comprising a piezoelectric substrate on which wave elements are arranged in multiple stages approximately parallel to each other, and a base on which the piezoelectric substrate is placed and in which a ground terminal and a signal terminal for electrical connection with an external circuit are implanted. In the surface acoustic wave device, a surface acoustic wave element disposed near one side of the piezoelectric substrate substantially parallel to the propagation direction of the surface acoustic wave excited from the excitation electrode is used as a first stage surface acoustic wave element, and a surface acoustic wave element disposed near the other side A surface acoustic wave element disposed in the first stage is a final stage surface acoustic wave element, and a positive comb-shaped electrode constituting the excitation electrode of the first stage surface acoustic wave element and the signal terminal are electrically connected. , a negative comb-shaped electrode constituting the excitation electrode of the first stage surface acoustic wave element and the connection terminal are electrically connected, and a positive electrode constituting the receiving electrode of the final stage surface acoustic wave element The comb-shaped electrode and the signal terminal are electrically connected, the negative comb-shaped electrode constituting the receiving electrode of the final stage surface acoustic wave element and the ground terminal are electrically connected, Except for the excitation electrode of the first stage surface acoustic wave element and the reception electrode of the final stage surface acoustic wave element, the excitation electrode of one of the surface acoustic wave elements and the other surface acoustic wave element adjacent thereto The receiving electrode of the element constitutes one set, and the comb-like electrodes forming the excitation electrode and the comb-like electrode forming the receiving electrode are electrically connected to each other. Surface acoustic wave device. (2) The surface acoustic wave device according to claim 1, wherein the surface acoustic wave elements are arranged on the same piezoelectric substrate. (3) The surface acoustic wave device according to claim 1, wherein the surface acoustic wave elements are arranged on individual piezoelectric substrates. (4) In claim 1, a connection point between the first stage surface acoustic wave element and the signal terminal and the ground terminal, and a connection between the final stage surface acoustic wave element and the signal terminal and the ground terminal. A surface acoustic wave device characterized in that a point is in a direction opposite to the piezoelectric substrate, and a connection point between the signal terminal and the ground terminal is in the same direction.